1. Field of the Invention
The present invention relates to electromagnetic actuator devices suitable for use in operating electrical switchgear, such as vacuum circuit breakers. The invention has particular, though not exclusive, relevance to direct current circuit breakers and vacuum circuit breakers in general.
2. Related Art
High power circuit breakers require large opening and closing forces to overcome various contact forces encountered. This requires the use of large and heavy actuators which are consequently much slower to operate than their smaller equivalents. This is disadvantageous, particularly in DC circuits where a fast circuit breaking action is required.
In addition, because the contacts of such circuit breakers tend to wear with use, it is desirable to include, in the circuit breaker mechanism, means to accommodate an increasing relative distance between the contact surfaces when open, ie. means to provide an increasing actuation distance during the lifespan of the contacts. This is typically achieved by providing an electromagnetic actuator which drives a moving contact through a closing spring coupling, which absorbs any difference between actuator stroke length and actual contact travel distance. This feature, however, results in the creation of a snatch gap which means that the actuator does not even start to open the contacts until part way through its opening stroke, thereby slowing still further the circuit breaking operation.
It is an object of the present invention to provide an improved circuit breaker providing high speed current interruption.